@paat So just to be clear, you have a Dell branded usbc cable?
I have a dell branded usb c ethernet adapter on a 7400 and I can pxe boot into the fog compatibility menu (I don’t want to image my workstation at the moment) and ping devices. So I know the network adapter works. Also when we image we typically use the WD15 dock (the WD19 docks are flaky some times with pxe booting). That way we charge the laptop as well as image at the same time.
This is the dell usbc dongle we are using: https://www.dell.com/en-us/shop/dell-adapter-usb-c-to-ethernet-pxe-boot/apd/470-abnd/pc-accessories
Also what version of FOG are you using as well as what FOS Linux kernel version do you have?